1. Field of the Invention
The present invention relates to a scanning module resolution adjustment method, and more particularly, to a resolution adjustment method for adjusting resolutions of a scanning module in two perpendicular directions.
2. Description of the Prior Art
Resolution of a scanning module is commonly adjusted by modifying the position of the lens in the scanning module. To find the correct position of the lens for generating an optimal resolution, image signals generated by scanning a calibration picture using the scanning module are used.
The resolution of a scanning module has a horizontal directional component and a vertical directional component. Optimal resolutions as well as the optimal positioning of the lens to obtain the best resolution in the two directions are different due to aberrations of the lens. Therefore, the lens has to be positioned at a position that allows both of the horizontal and vertical resolutions to approach the optimal state.
The calibration picture used to calibrate the scanning module comprises a group of parallel vertical lines or slanted lines. The vertical lines generate images used to adjust the vertical resolution but not the horizontal resolution. Therefore, the vertical lines are appropriate only for calibrating a lens with identical horizontal and vertical resolutions. Slanted lines, on the other hand, generate images comprising both the vertical and horizontal resolutions. However, if the slanted lines incline more horizontally than vertically, the horizontal component will predominate and use of the generated image alone cannot separately calibrate the vertical and horizontal resolutions. Therefore, it may be very difficult to find the ideal position of the lens. This in turn lowers the yield.